<?php
class ImageHash {
      
    const FILE_NOT_FOUND = '-1';
    const FILE_EXTNAME_ILLEGAL = '-2';
      
    private function __construct() {}
      
    public static function run($src1, $src2) {
          
        static $self;
        if(!$self) $self = new static;
          
        if(!is_file($src1) || !is_file($src2)) exit(self::FILE_NOT_FOUND);
  
        $hash1 = $self->getHashValue($src1);
        $hash2 = $self->getHashValue($src2);
          
        if(strlen($hash1) !== strlen($hash2)) return false;
          
        $count = 0;
        $len = strlen($hash1);
        for($i = 0; $i < $len; $i++) if($hash1[$i] !== $hash2[$i]) $count++;
        return $count <= 10 ? true : false;
  
    }
      
    public function getImage($file) {
          
        $extname = pathinfo($file, PATHINFO_EXTENSION);
        if(!in_array($extname, ['jpg','jpeg','png','gif'])) exit(self::FILE_EXTNAME_ILLEGAL);
        $img = call_user_func('imagecreatefrom'. ( $extname == 'jpg' ? 'jpeg' : $extname ) , $file);
        return $img;
          
    }
      
    public function getHashValue($file) {
          
        $w = 8;
        $h = 8;
        $img = imagecreatetruecolor($w, $h);
        list($src_w, $src_h) = getimagesize($file);
        $src = $this->getImage($file);
        imagecopyresampled($img, $src, 0, 0, 0, 0, $w, $h, $src_w, $src_h);
        imagedestroy($src);
          
        $total = 0;
        $array = array();
        for( $y = 0; $y < $h; $y++) {
            for ($x = 0; $x < $w; $x++) {
                $gray = (imagecolorat($img, $x, $y) >> 8) & 0xFF;
                if(!isset($array[$y])) $array[$y] = array();
                $array[$y][$x] = $gray;
                $total += $gray;
            }
        }
          
        imagedestroy($img);
          
        $average = intval($total / ($w * $h * 2));
        $hash = '';
        for($y = 0; $y < $h; $y++) {
            for($x = 0; $x < $w; $x++) {
                $hash .= ($array[$y][$x] >= $average) ? '1' : '0';
            }
        }
          
        var_dump($hash);
        return $hash;
          
    }
      
}
var_dump(ImageHash::run('1.jpg', '4.jpg'));